Spectral imaging, in particular hyperspectral imaging in which each pixel contains a high-resolution spectrum, has proven to be valuable for remote detection, identification and quantification of chemical species, in applications ranging from proliferation detection to environmental monitoring, planetary science, and medical imaging. The spectral content of each pixel is typically analyzed for the presence of various chemicals or materials of interest which have spectral signatures in the spectral region investigated. As currently implemented, hyperspectral imaging is inherently slow, typically requiring several seconds to obtain a single image. Monitoring phenomena occurring on timescales faster than this has necessitated sacrificing either spectral specificity (that is, reducing the spectral component to a simple band-pass filter in front of a fast camera), or sacrificing spatial information and simply aiming a spectrometer at a point (or, at most, a line). Both of these options are unsatisfactory for a variety of reasons.
One existing programmable HSI system is described in “Programmable Matched Filter And Hadamard Transform Hyperspectral Imagers Based On Micro-Mirror Arrays” by Steven P. Love, Proc. of SPIE, Vol. 7210, 721007 (2009), the entirety of the disclosure and teachings of which document are hereby specifically incorporated by reference herein. Unfortunately, the Love programmable HSI must either scan the spectral patterns across the MMA or scan the direction of aiming of the instrument to produce a full two-dimensional spatial image having the desired spectral processing. As such, the development of a programmable spectral filter had been stymied by the intertwining of spatial and spectral directions that is a feature of nearly all imaging spectrometer designs. Accordingly, there is a need for an improved full-framed hyperspectral imaging apparatus and/or system. As described in detail below, embodiments of the present invention overcome the disadvantages and limitations of the state of the art by providing an apparatus for obtaining a full-frame hyperspectral image without the requirement of either an external push-broom scan or of scanning the image on the micro-mirror array in order to generate spectral/spatial information wherein the spectral data is properly associated with the spatial data.
A preferred embodiment of the present invention can include an initial optical subsystem receiving incident light and generating an image including spatially invariant light propagation defining a substantially spatially invariant angle of incidence at a first predetermined location having an image plane; a dispersive element disposed at the predetermined location to receive the image at the substantially spatially invariant angle of incidence and to generate wavelength dispersed light; and a second optical subsystem receiving the wavelength dispersed light and generating a spatially dispersed spectrum at a second predetermined location such that in at least one dimension of a spectral plane, substantially all light of a predetermined wavelength is directed to a substantially identical position within the spectral plane. The preferred apparatus can further include a selective element disposed at the second predetermined location and optically coupled to the dispersive element, the selective element configured to programmably modulate an amplitude of light at one or more locations in the spectral plane to produce spectrally modified light; and a detector receiving the spectrally modified light from the selective element. As described below, preferably the spectrally modified light includes an image representation of the incident light in which the spectral content has been modified by the selective element in one or more spectral bands, and further preferably such spectral modification is substantially identical for substantially all locations in the image representation.
Benefits and advantages of embodiments of the present invention include, but are not limited to, providing an apparatus for performing full spatial frame micro-mirror-array-based spectral processing without wavelength shifts over the entire two-dimensional image, wherein spectral imaging can be performed without scanning and at speeds limited only by the detector employed. Compared to current hyperspectral imaging devices, the imaging time for a given area for embodiments of the present invention potentially can be reduced by factors of several hundred.